Estep Laura K, Sackett Kathryn E, Mundt Christopher C
Ecol Appl. 2014;24(7):1854-62. doi: 10.1890/13-1408.1.
Pathogen invasions pose a growing threat to ecosystem stability and public health. Guidelines for the timing and spatial extent of control measures for pathogen invasions are currently limited, however. We conducted a field experiment using wheat (Triticum aestivum) stripe rust, caused by the wind-dispersed fungus Puccinia striiformis, to study the extent to which host heterogeneity in an initial outbreak focus influences subsequent disease spread. We varied the frequency of susceptible host plants in an initial outbreak focus and in the non-focus of experimental plots, and observed the progress of epidemics produced by artificial inoculation. The frequency of susceptible hosts in the initial outbreak focus increased the spread of stripe rust in the experimental plots, while frequency of susceptible hosts outside the initial outbreak focus did not. This suggests that factors influencing pathogen reproduction in the initial outbreak focus are key to the control of epidemics of stripe rust. Two mechanisms may underlie the field results. The first is the continuing, direct infection of susceptible hosts in areas outside the initial outbreak focus by disease propagules arriving from the initial outbreak focus. The second is highly local proliferation of disease caused by direct descendants of colonizing individuals originating from the initial outbreak focus. We considered these two alternatives in simulations of a generalized pathogen exhibiting fat-tailed dispersal, similar to P. striiformis. Simulations showed a dominant effect of conditions in the initial outbreak focus, in agreement with the field experiment, but indicated that, over time, this dominance may erode. Analysis of the duration of focal dominance led to the conclusion that both mechanisms contribute to the phenomenon of focal dominance, and that the frequency of susceptible hosts in the initial outbreak focus had a stronger influence when the proportion of propagules that remained local during dispersal was higher. Overall, our results suggest that targeting pathogen reproduction in the initial outbreak focus will have a disproportionately large impact on subsequent epidemic spread.
病原体入侵对生态系统稳定性和公众健康构成了日益严重的威胁。然而，目前关于病原体入侵控制措施的时间和空间范围的指导方针还很有限。我们利用由风传播的真菌条锈菌引起的小麦条锈病进行了一项田间试验，以研究初始发病中心的宿主异质性对后续病害传播的影响程度。我们改变了试验小区初始发病中心和非发病中心易感宿主植物的频率，并观察了人工接种引发的病害流行进程。初始发病中心易感宿主的频率增加了试验小区条锈病的传播，而初始发病中心以外的易感宿主频率则没有这种作用。这表明，影响初始发病中心病原体繁殖的因素是控制条锈病流行的关键。田间试验结果可能基于两种机制。第一种是来自初始发病中心的病害传播体持续直接感染初始发病中心以外区域的易感宿主。第二种是由初始发病中心定殖个体的直接后代引起的病害高度局部增殖。我们在模拟一种表现出肥尾扩散的广义病原体（类似于条锈菌）时考虑了这两种可能性。模拟结果显示，初始发病中心的条件具有主导作用，这与田间试验结果一致，但表明随着时间的推移，这种主导作用可能会减弱。对发病中心主导期持续时间的分析得出结论，两种机制都促成了发病中心主导现象，并且当传播过程中保持在局部的传播体比例较高时，初始发病中心易感宿主的频率影响更强。总体而言，我们的结果表明，针对初始发病中心的病原体繁殖进行防控将对后续的病害流行传播产生 disproportionately large impact。 （最后一句中“disproportionately large impact”直译为“不成比例的巨大影响”，结合语境这里可灵活处理为“极大的影响” ，但题目要求不添加任何解释或说明，所以保留原文）
